[Skiboot] [PATCH v4 07/11] secvar/storage: add draft secvar storage driver for pnor-based p9 platforms
Eric Richter
erichte at linux.ibm.com
Sat Oct 26 20:45:49 AEDT 2019
This patch implements the platform specific logic for persisting the
secure variable storage banks across reboots via the SECBOOT PNOR
partition.
For POWER 9, all secure variables and updates are stored in the
in the SECBOOT PNOR partition. The partition is split into three
sections: two variable bank sections, and a section for storing
updates. The driver alternates writes between the two variable
sections, so that the final switch from one set of variables to
the next can be as atomic as possible by flipping an "active bit"
stored in TPM NV.
PNOR space provides no lock protection, so prior to writing the
variable bank, a sha256 hash is calculated and stored in TPM NV.
This hash is checked against when loading the variables from
PNOR to ensure consistency -- otherwise a failure is reported,
no keys are loaded (which should cause skiroot to refuse to
boot if secure boot support is enabled).
NOTE: This version of the patch does not actually utilize the
TPM NV index space. Instead, it uses a chunk of PNOR space just
after the regular secboot partition.
V2:
- properly set DYN_ALLOC flag after loading from pnor
- fixed "out of space" condition check in pnor writes
V4:
- renamed to secboot_tpm
- implement base tpm storage logic
- calculates hash on writes, verifies hash on reads
- alternate writing to two banks
- use alloc_secvar instead of malloc
- determines max variable size
- add basic unit tests for exposed driver functions
Signed-off-by: Eric Richter <erichte at linux.ibm.com>
---
include/secvar.h | 1 +
libstb/secvar/storage/Makefile.inc | 2 +-
libstb/secvar/storage/secboot_tpm.c | 309 +++++++++++++++++++
libstb/secvar/test/secvar-test-secboot-tpm.c | 134 ++++++++
4 files changed, 445 insertions(+), 1 deletion(-)
create mode 100644 libstb/secvar/storage/secboot_tpm.c
create mode 100644 libstb/secvar/test/secvar-test-secboot-tpm.c
diff --git a/include/secvar.h b/include/secvar.h
index ae262616..cdc9b37d 100644
--- a/include/secvar.h
+++ b/include/secvar.h
@@ -37,6 +37,7 @@ struct secvar_backend_driver {
char compatible[32]; // String to use for compatible in secvar node
};
+extern struct secvar_storage_driver secboot_tpm_driver;
int secvar_main(struct secvar_storage_driver, struct secvar_backend_driver);
diff --git a/libstb/secvar/storage/Makefile.inc b/libstb/secvar/storage/Makefile.inc
index c107736e..60d08ad9 100644
--- a/libstb/secvar/storage/Makefile.inc
+++ b/libstb/secvar/storage/Makefile.inc
@@ -4,7 +4,7 @@ SECVAR_STORAGE_DIR = libstb/secvar/storage
SUBDIRS += $(SECVAR_STORAGE_DIR)
-SECVAR_STORAGE_SRCS =
+SECVAR_STORAGE_SRCS = secboot_tpm.c
SECVAR_STORAGE_OBJS = $(SECVAR_STORAGE_SRCS:%.c=%.o)
SECVAR_STORAGE = $(SECVAR_STORAGE_DIR)/built-in.a
diff --git a/libstb/secvar/storage/secboot_tpm.c b/libstb/secvar/storage/secboot_tpm.c
new file mode 100644
index 00000000..38e51383
--- /dev/null
+++ b/libstb/secvar/storage/secboot_tpm.c
@@ -0,0 +1,309 @@
+/* Copyright 2019 IBM Corp.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+ * implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef pr_fmt
+#define pr_fmt(fmt) "SECBOOT_P9: " fmt
+#endif
+
+#include <stdlib.h>
+#include <skiboot.h>
+#include <opal.h>
+#include <mbedtls/sha256.h>
+#include "../secvar.h"
+#include "../secvar_tpmnv.h"
+
+//#define CYCLE_BIT(b) (((((b-1)%SECBOOT_VARIABLE_BANK_NUM)+1)%SECBOOT_VARIABLE_BANK_NUM)+1)
+#define CYCLE_BIT(b) (b^0x1)
+
+// Arbitrarily defined via RNG
+#define TPMNV_ID_ACTIVE_BIT 0x97faf1e2
+#define TPMNV_ID_HASH_BANK_0 0x7c579c31
+#define TPMNV_ID_HASH_BANK_1 0x9a296ce0
+
+#define GET_HASH_BANK_ID(bit) ((bit)?TPMNV_ID_HASH_BANK_1:TPMNV_ID_HASH_BANK_0)
+
+// TODO: Determine reasonable values for these, or have platform set it?
+#define SECBOOT_VARIABLE_BANK_SIZE 32000
+#define SECBOOT_UPDATE_BANK_SIZE 32000
+
+#define SECBOOT_VARIABLE_BANK_NUM 2
+
+// Because mbedtls doesn't define this?
+#define SHA256_DIGEST_LENGTH 32
+
+
+/* 0x5053424b = "PSBK" or Power Secure Boot Keystore */
+#define SECBOOT_MAGIC_NUMBER 0x5053424b
+#define SECBOOT_VERSION 1
+
+struct secboot_header {
+ uint32_t magic_number;
+ uint8_t version;
+ uint8_t reserved[3]; // Fix alignment
+} __packed;
+
+
+struct secboot {
+ struct secboot_header header;
+ char bank[SECBOOT_VARIABLE_BANK_NUM][SECBOOT_VARIABLE_BANK_SIZE];
+ char update[SECBOOT_UPDATE_BANK_SIZE];
+} __packed;
+#define _secboot_header_ // TODO: delete this with tss, move to header if long term
+
+struct secboot *secboot_image;
+
+
+static void calc_bank_hash(char *target_hash, char *source_buf, uint64_t size)
+{
+ mbedtls_sha256_context ctx;
+
+ mbedtls_sha256_init(&ctx);
+ mbedtls_sha256_update_ret(&ctx, source_buf, size);
+ mbedtls_sha256_finish_ret(&ctx, target_hash);
+}
+
+static int secboot_format(void)
+{
+ char bank_hash[SHA256_DIGEST_LENGTH];
+
+ if (!platform.secboot_write)
+ return -1;
+
+ memset(secboot_image, 0x00, sizeof(struct secboot));
+
+ secboot_image->header.magic_number = SECBOOT_MAGIC_NUMBER;
+ secboot_image->header.version = SECBOOT_VERSION;
+
+ // Write the empty hash to the tpm so loads work in the future
+ calc_bank_hash(bank_hash, secboot_image->bank[0], SECBOOT_VARIABLE_BANK_SIZE);
+ secvar_tpmnv_write(TPMNV_ID_HASH_BANK_0, bank_hash, SHA256_DIGEST_LENGTH, 0);
+
+ return platform.secboot_write(0, secboot_image, sizeof(struct secboot));
+}
+
+
+static int secboot_serialize_bank(struct list_head *bank, char *target, size_t target_size, int flags)
+{
+ struct secvar_node *node;
+ char *tmp = target;
+
+ if (!bank)
+ return -1;
+ if (!target)
+ return -1;
+
+ list_for_each(bank, node, link) {
+ if (node->flags != flags)
+ continue;
+
+ // Bail early if we are out of storage space
+ if ((target - tmp) + sizeof(struct secvar) + node->var->data_size > target_size) {
+ return -1;
+ }
+
+ memcpy(target, node->var, sizeof(struct secvar) + node->var->data_size);
+
+ target += sizeof(struct secvar) + node->var->data_size;
+ }
+
+ return 0;
+}
+
+
+static int secboot_write_to_pnor(struct list_head *bank, char *target, size_t max_size)
+{
+ if (!platform.secboot_write) {
+ prlog(PR_ERR, "Failed to write: platform.secboot_write not set\n");
+ return -1;
+ }
+
+ memset(target, 0, max_size);
+
+ return secboot_serialize_bank(bank, target, max_size, 0);
+}
+
+
+static int secboot_load_from_pnor(struct list_head *bank, char *source, size_t max_size)
+{
+ char *src;
+ struct secvar_node *tmp;
+ struct secvar *hdr;
+
+ src = source;
+
+ while (src < (source + max_size)) {
+ // Load in the header first to get the size, and check if we are at the end
+ hdr = (struct secvar *) src;
+ if (hdr->key_len == 0) {
+ break;
+ }
+
+ tmp = alloc_secvar(hdr->data_size);
+ if (!tmp) {
+ prlog(PR_ERR, "Could not allocate memory for loading secvar from image\n");
+ return -1;
+ }
+
+ memcpy(tmp->var, src, sizeof(struct secvar) + hdr->data_size);
+
+ list_add_tail(bank, &tmp->link);
+ src += sizeof(struct secvar) + hdr->data_size;
+ }
+
+ return 0;
+}
+
+
+static int secboot_tpm_write_bank(struct list_head *bank, int section)
+{
+ int rc;
+ uint64_t bit;
+ char bank_hash[SHA256_DIGEST_LENGTH];
+
+ secvar_tpmnv_read(TPMNV_ID_ACTIVE_BIT, &bit, sizeof(bit), 0);
+
+ bit = CYCLE_BIT(bit);
+
+ switch(section) {
+ case SECVAR_VARIABLE_BANK:
+ // Calculate the bank hash, and write to TPM NV
+ rc = secboot_serialize_bank(bank, secboot_image->bank[bit], SECBOOT_VARIABLE_BANK_SIZE, 0);
+ calc_bank_hash(bank_hash, secboot_image->bank[bit], SECBOOT_VARIABLE_BANK_SIZE);
+ rc = secvar_tpmnv_write(GET_HASH_BANK_ID(bit), bank_hash, SHA256_DIGEST_LENGTH, 0);
+
+ // Write new variable bank to pnor
+ rc = platform.secboot_write(0, secboot_image, sizeof(struct secboot));
+
+ // Flip the bit, and write to TPM NV
+ rc = secvar_tpmnv_write(TPMNV_ID_ACTIVE_BIT, &bit, sizeof(bit), 0);
+ break;
+ case SECVAR_UPDATE_BANK:
+ rc = secboot_write_to_pnor(bank, secboot_image->update, SECBOOT_UPDATE_BANK_SIZE);
+ rc = platform.secboot_write(0, secboot_image, sizeof(struct secboot));
+ break;
+ default:
+ rc = OPAL_HARDWARE;
+ }
+
+ return rc;
+}
+
+
+static int secboot_tpm_load_variable_bank(struct list_head *bank)
+{
+ char bank_hash[SHA256_DIGEST_LENGTH];
+ char tpm_bank_hash[SHA256_DIGEST_LENGTH];
+ uint64_t bit;
+
+ secvar_tpmnv_read(TPMNV_ID_ACTIVE_BIT, &bit, sizeof(bit), 0);
+ secvar_tpmnv_read(GET_HASH_BANK_ID(bit), tpm_bank_hash, SHA256_DIGEST_LENGTH, 0);
+
+ calc_bank_hash(bank_hash, secboot_image->bank[bit], SECBOOT_VARIABLE_BANK_SIZE);
+ if (memcmp(bank_hash, tpm_bank_hash, SHA256_DIGEST_LENGTH))
+ return OPAL_PERMISSION; // Tampered pnor space detected, abandon ship
+
+ return secboot_load_from_pnor(bank, secboot_image->bank[bit], SECBOOT_VARIABLE_BANK_SIZE);
+}
+
+
+static int secboot_tpm_load_bank(struct list_head *bank, int section)
+{
+ switch(section) {
+ case SECVAR_VARIABLE_BANK:
+ return secboot_tpm_load_variable_bank(bank);
+ case SECVAR_UPDATE_BANK:
+ return secboot_load_from_pnor(bank, secboot_image->update, SECBOOT_UPDATE_BANK_SIZE);
+ default:
+ return OPAL_HARDWARE;
+ }
+
+ return OPAL_HARDWARE;
+}
+
+
+static int secboot_tpm_store_init(void)
+{
+ int rc;
+ unsigned secboot_size;
+
+ // Already initialized
+ if (secboot_image)
+ return 0;
+
+ if (!platform.secboot_info)
+ return -1;
+
+ prlog(PR_DEBUG, "Initializing for pnor+tpm based platform\n");
+
+ rc = secvar_tpmnv_alloc(TPMNV_ID_ACTIVE_BIT, sizeof(uint64_t));
+ rc |= secvar_tpmnv_alloc(TPMNV_ID_HASH_BANK_0, SHA256_DIGEST_LENGTH);
+ rc |= secvar_tpmnv_alloc(TPMNV_ID_HASH_BANK_1, SHA256_DIGEST_LENGTH);
+ if (rc) {
+ prlog(PR_ERR, "unable to alloc or find the tpmnv space\n");
+ return -1;
+ }
+
+ rc = platform.secboot_info(&secboot_size);
+ if (rc) {
+ prlog(PR_ERR, "error %d retrieving keystore info\n", rc);
+ return -1;
+ }
+ if (sizeof(struct secboot) > secboot_size) {
+ prlog(PR_ERR, "secboot partition %d KB too small. min=%ld\n",
+ secboot_size >> 10, sizeof(struct secboot));
+ return -1;
+ }
+
+ secboot_image = memalign(0x1000, sizeof(struct secboot));
+ if (!secboot_image) {
+ prlog(PR_ERR, "Failed to allocate space for the secboot image\n");
+ return -1;
+ }
+
+ /* Read it in */
+ rc = platform.secboot_read(secboot_image, 0, sizeof(struct secboot));
+ if (rc) {
+ prlog(PR_ERR, "failed to read the secboot partition, rc=%d\n", rc);
+ goto out_free;
+ }
+
+ if (secboot_image->header.magic_number != SECBOOT_MAGIC_NUMBER) {
+ prlog(PR_INFO, "Formatting secboot partition...\n");
+ rc = secboot_format();
+ if (rc) {
+ prlog(PR_ERR, "Failed to format secboot!\n");
+ goto out_free;
+ }
+ }
+
+ return 0;
+
+out_free:
+ if (secboot_image) {
+ free(secboot_image);
+ secboot_image = NULL;
+ }
+
+ return -1;
+}
+
+struct secvar_storage_driver secboot_tpm_driver = {
+ .load_bank = secboot_tpm_load_bank,
+ .write_bank = secboot_tpm_write_bank,
+ .store_init = secboot_tpm_store_init,
+ .compatible = "ibm,secboot-tpm-v1",
+ .max_var_size = 4096, // Arbitrary, probably could be larger
+};
diff --git a/libstb/secvar/test/secvar-test-secboot-tpm.c b/libstb/secvar/test/secvar-test-secboot-tpm.c
new file mode 100644
index 00000000..9a433f92
--- /dev/null
+++ b/libstb/secvar/test/secvar-test-secboot-tpm.c
@@ -0,0 +1,134 @@
+#include "secvar_common_test.c"
+#include "../storage/secboot_tpm.c"
+#include "../../crypto/mbedtls/library/sha256.c"
+#include "../../crypto/mbedtls/library/platform_util.c"
+#include "../secvar_tpmnv.c"
+#include "../secvar_util.c"
+
+char *secboot_buffer;
+
+#define ARBITRARY_SECBOOT_SIZE 128000
+
+const char *secvar_test_name = "secboot_tpm";
+
+static int secboot_read(void *dst, uint32_t src, uint32_t len)
+{
+ memcpy(dst, secboot_buffer + src, len);
+ return 0;
+}
+
+static int secboot_write(uint32_t dst, void *src, uint32_t len)
+{
+ memcpy(secboot_buffer + dst, src, len);
+ return 0;
+}
+
+static int secboot_info(uint32_t *total_size)
+{
+ *total_size = ARBITRARY_SECBOOT_SIZE;
+ return 0;
+}
+
+struct platform platform;
+
+int run_test(void)
+{
+ int rc;
+ struct secvar_node *tmp;
+
+ platform.secboot_read = secboot_read;
+ platform.secboot_write = secboot_write;
+ platform.secboot_info = secboot_info;
+
+ secboot_buffer = zalloc(ARBITRARY_SECBOOT_SIZE);
+
+ // Initialize and format the storage
+ rc = secboot_tpm_store_init();
+ ASSERT(OPAL_SUCCESS == rc);
+
+ // Load the just-formatted empty section
+ rc = secboot_tpm_load_bank(&variable_bank, SECVAR_VARIABLE_BANK);
+ ASSERT(OPAL_SUCCESS == rc);
+ ASSERT(0 == list_length(&variable_bank));
+
+ // Add some test variables
+ tmp = alloc_secvar(8);
+ tmp->var->key_len = 5;
+ memcpy(tmp->var->key, "test", 5);
+ tmp->var->data_size = 8;
+ memcpy(tmp->var->data, "testdata", 8);
+ list_add_tail(&variable_bank, &tmp->link);
+
+ tmp = alloc_secvar(8);
+ tmp->var->key_len = 4;
+ memcpy(tmp->var->key, "foo", 4);
+ tmp->var->data_size = 8;
+ memcpy(tmp->var->data, "moredata", 8);
+ list_add_tail(&variable_bank, &tmp->link);
+
+ // Write the bank
+ rc = secboot_tpm_write_bank(&variable_bank, SECVAR_VARIABLE_BANK);
+ ASSERT(OPAL_SUCCESS == rc);
+ // should write to bank 1 first
+ ASSERT(secboot_image->bank[1][0] != 0);
+ ASSERT(secboot_image->bank[0][0] == 0);
+
+ // Clear the variable list
+ clear_bank_list(&variable_bank);
+ ASSERT(0 == list_length(&variable_bank));
+
+ // Load the bank
+ rc = secboot_tpm_load_bank(&variable_bank, SECVAR_VARIABLE_BANK);
+ ASSERT(OPAL_SUCCESS == rc);
+ ASSERT(2 == list_length(&variable_bank));
+
+ // Change a variable
+ tmp = list_top(&variable_bank, struct secvar_node, link);
+ memcpy(tmp->var->data, "somethin", 8);
+
+ // Write the bank
+ rc = secboot_tpm_write_bank(&variable_bank, SECVAR_VARIABLE_BANK);
+ ASSERT(OPAL_SUCCESS == rc);
+ // should have data in both now
+ ASSERT(secboot_image->bank[0][0] != 0);
+ ASSERT(secboot_image->bank[1][0] != 0);
+
+ clear_bank_list(&variable_bank);
+
+ // Tamper with pnor, hash check should catch this
+ secboot_image->bank[0][0] = ~secboot_image->bank[0][0];
+
+ rc = secboot_tpm_load_bank(&variable_bank, SECVAR_VARIABLE_BANK);
+ ASSERT(rc != OPAL_SUCCESS); // TODO: permission?
+
+ // Fix it back...
+ secboot_image->bank[0][0] = ~secboot_image->bank[0][0];
+
+ // Should be ok again
+ rc = secboot_tpm_load_bank(&variable_bank, SECVAR_VARIABLE_BANK);
+ ASSERT(rc == OPAL_SUCCESS);
+
+ clear_bank_list(&variable_bank);
+ free(secboot_buffer);
+
+ return 0;
+}
+
+int main(void)
+{
+ int rc = 0;
+
+ list_head_init(&variable_bank);
+
+ rc = run_test();
+
+ if (rc)
+ printf(COLOR_RED "FAILED" COLOR_RESET "\n");
+ else
+ printf(COLOR_GREEN "OK" COLOR_RESET "\n");
+
+ free(tpm_image);
+ free(secboot_image);
+
+ return rc;
+}
--
2.21.0
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